CN102076006B - Method for detecting PRACH preamble signal - Google Patents

Abstract

The invention discloses a method for detecting a physical random access channel (PRACH) preamble signal, which mainly aims at the situation that four antennae are adopted for receiving in an uplink of a long term evolution (LTE) system. The method comprises the following steps of: determining an approximate straight line representing a relationship between a false alarm probability and a false alarm threshold; for the given false alarm probability, resolving a false alarm threshold T which is not corrected according to the approximate straight line; selecting a group of sequence z(n) with thelength of Ns in output signals which are obtained through incoherent combination of signals received by a receiver, and removing a few maximum values in the sequence z(n) according to simulation experience to obtain a result sequence in which the length Ns is a time slot length, or a sub-frame length or length of a plurality of sub-frames; resolving the corrected false alarm threshold according to a correction relationship of the false alarm threshold, and determining that a random access request exists in a received signal when a value which is greater than the corrected false alarm threshold exists in the sequence z(n). Through the method, the effective false alarm threshold can be easily and quickly acquired.

Description

A kind of method that detects the PRACH targeting signal

Technical field

The present invention relates to the 3rd third-generation mobile communication Long Term Evolution (LTE) system, adopt for the LTE system up-link and to adopt in 4 reception antennas or the follow-up evolution system more in the multiple receive antenna situation, in the method that detects LTE ascending physical signal Random Access Channel (PRACH) targeting signal.

Background technology

In the 3rd third-generation mobile communication Long Term Evolution (LTE) system, the user is after the start completion system is synchronous, when connecting system, launch a targeting signal that is produced by Zadoff-Chu sequence (generally also be called for short the ZC sequence, the document 3GPP TS 36.211V8.5.0 of 3GPPLTE standard is seen in its detailed explanation) cyclic shift to receiver in ascending physical signal Random Access Channel (PRACH).Receiver has judged whether that by detecting the PRACH targeting signal user asks access in the signal of receiving.

The process of receiver detection PRACH targeting signal supposes to have a plurality of reception antennas, reception antenna T as shown in Figure 1 _iThe baseband signal x that receives _iAt first reduce sampling rate through low-pass filtering and extraction, then (result of related operation is one group of sequence of complex numbers to carry out related operation with local ZC sequence in correlator, the detailed content of related operation does not belong to content of the present invention), the result of related operation is asked behind the absolute value square again output power stage range signal y _iThen after each road power level magnitudes signal being carried out incoherent merging, output power stage amplitude sequence, the threshold value of this amplitude sequence and receiver setting compares, if the threshold value that has a peak value to arrange greater than receiver in this amplitude sequence, then judging has the user to ask access.

To the situation of single antenna and 2 antenna receptions, arranging of receiver threshold value is fairly simple, and the present invention does not relate to.The setting of receiver threshold when the present invention relates generally to the uplink random access signal that adopts 4 antenna receptions.When the following describes in the prior art for 4 antennas, how receiver arranges thresholding.

During 4 antenna reception, behind 4 road absolute values again square after the power level magnitudes signal y of output ₁, y ₂, y ₃, y ₄In contained white Gaussian noise be plural number, real part and imaginary part satisfy respectively independently Gaussian Profile, real part quadratic sum imaginary part square and to satisfy the degree of freedom be 2 Chi square distribution.The power level magnitudes signal y of 4 tunnel outputs ₁, y ₂, y ₃, y ₄Carry out incoherent merging, following formula is adopted in incoherent merging:

y＝y ₁+y ₂+y ₃+y ₄ (1)

(1) in the formula, y represents the output after the incoherent merging, and its sample sequence is the power level magnitudes sequence.

Containing in the situation about transmitting, the additive white Gaussian noise power level magnitudes sequence that comprises in this sequence, it is 8 Chi square distribution that the stochastic variable y that represents this sequence satisfies the degree of freedom;

Do not containing in the situation about transmitting, the sample sequence of y is Gaussian sequence, and it is 8 Chi square distribution that the stochastic variable y that represents this sequence amplitude satisfies the degree of freedom.

The degree of freedom is that the probability density function of the stochastic variable y of k is defined as:

$f(y;k)=\frac{1}{2^{k/2}\mathrm{\Γ}(k/2)}{y}^{k/2-1}{e}^{-y/2}---\left(2\right)$

(2) in the formula, f (y; K) the expression degree of freedom is the probability density function of the stochastic variable y of k, and e is the substrate of natural logrithm, and Г () is gamma function.For the receiving system of 4 antennas, k=8.

The cumulant distribution function of corresponding (2) formula is:

F(y，k)＝1-P _fa(y，k) (3)

(3) in the formula, y is identical with the definition in (2) with k, P _Fa(y, k) is that the degree of freedom is the false alarm probability of the stochastic variable y of k.

The degree of freedom is the false alarm probability P of the stochastic variable y of k _FaThe calculating formula of (y, k) is:

$P_{\mathrm{fa}}(y,k)=\underset{i=0}{\overset{k/2-1}{\mathrm{\Σ}}}\frac{{(y/2)}^i}{i!}{e}^{-y/2}---\left(4.1\right)$

(4.1) in the formula, "! " computing of expression factorial.When k=8, can be got by (4.1):

P _fa(y，8)＝e ^-y/2(1+y/2+y ²/8+y ³/48) (4.2)

If not relevant the merging adopts:

z＝(y ₁+y ₂+y ₃+y ₄)/4＝y/4 (5.1)

Then, (4.2) formula can be rewritten into following (5.2) formula:

P _fa(z，8)＝e ^-2z(1+2z+2z ²+4z ³/3) (5.2)

False alarm probability P for system's expectation _Fa(z, 8), (5.2) formula of solution can be obtained the z value as the false-alarm thresholding, and finding the solution of (5.2) formula needs to separate a nonlinear equation, amount of calculation is complicated.Whether have access request at first to need to calculate the false-alarm thresholding owing to judging in the signal that receiver receives, therefore the method for existing detection PRACH targeting signal is too complicated, so to be necessary to provide a kind of method of the simple PRACH of detection targeting signal.

Summary of the invention

The method that the purpose of this invention is to provide a kind of PRACH of detection targeting signal can be obtained the false-alarm thresholding quickly and easily, makes according to this false-alarm thresholding to judge in the signal that receiver receives whether have access request comparatively simple.

To achieve these goals, the invention provides a kind of method of the PRACH of detection targeting signal, comprise the steps:

(1) to the relational expression P of false alarm probability and false-alarm thresholding _Fa(z)=e ^-2z(1+2z+2z ²+ 4z ³/ 3) take the logarithm in both sides, obtains both logarithmic relationship formulas, wherein P _Fa(z, k) is false alarm probability, and z is the false-alarm thresholding;

(2) determine the near linear of the curve that the logarithmic relationship formula of false alarm probability and false-alarm thresholding represents;

(3) to given false alarm probability, find the solution the front false-alarm thresholding of correction according to described near linear;

(4) get that length is N in the output signal of signal after incoherent merging that receiver receives _sOne group of sequence z (n), remove several maximums among the sequence z (n) according to the emulation experience, obtain as a result sequence

Length N wherein _sSize be a slot length or a subframe lengths or a plurality of subframe lengths;

(5) according to the correction relational expression of false-alarm thresholding

Find the solution revised false-alarm thresholding, wherein T is the false-alarm thresholding before revising, T _FaBe revised false-alarm thresholding;

(6) when the value that has among the described sequence z (n) greater than described revised false-alarm thresholding, judging to receive in the signal has random access request.

In one embodiment of the invention, take the logarithm in the described step (1) to be specially and take from right logarithm or common logarithm.

Compared with prior art, the method that the present invention detects the PRACH targeting signal obtains the near linear of false alarm probability and false-alarm thresholding relation by step (1) and step (2), like this for set false alarm probability, it is very simple to find the solution the false-alarm thresholding, so that judge in the signal that receiver receives whether have access request comparatively simple according to this false-alarm thresholding.

In addition, this method is revised the false-alarm thresholding by the correction relational expression of step (5), with the actual noise (variance of real part and imaginary part differs and is decided to be 1) that satisfies relevant output corresponding to receiver reception antenna, improved the accuracy that this method detects.

By following description also by reference to the accompanying drawings, it is more clear that the present invention will become, and these accompanying drawings are used for explaining embodiments of the invention.

Description of drawings

Fig. 1 is the schematic diagram of LTE downlink physical layer processing procedure.

Fig. 2 has showed that the present invention detects theoretical logarithm false alarm probability curve and near linear in the method for PRACH targeting signal.

Fig. 3 is the flow chart that the present invention detects the method for PRACH targeting signal.

Embodiment

With reference now to accompanying drawing, describe embodiments of the invention, similar element numbers represents similar element in the accompanying drawing.

Before explanation false-alarm thresholding computational methods of the present invention, the principle that false-alarm thresholding of the present invention calculates is described first.

By common logarithm is got on formula (5.2) both sides, can get

log ₁₀P _fa(z，8)＝log ₁₀[e ^-2z(1+2z+2z ²+4z ³/3)] (6)

Log in (6) formula of picture ₁₀P _Fa(z, 8) see the curve among Fig. 2 with respect to the curve chart of z, this curve in a very large interval, log ₁₀P _Fa(z, 8) are almost the linear function of z, and for the LTE system, the false alarm probability P of its system's expectation _Fa(z, 8) are general all in the part of the near linear of this curve.

Like this, select two points of near linear part, as the curve that straight line comes approximate expression (6) to represent, the straight line that we adopt is:

log ₁₀(P _fa(T))＝-0.6421T+1.1059 (7)

(7) in the formula, T represents false-alarm thresholding, P _Fa(T) expression false alarm probability.

Draw the straight line of formula (7) expression in Fig. 2, such as Fig. 2 cathetus, can find out, this straight line is in a very large zone of the curve of formula (6) expression, well the curve of approximant (6) expression.Therefore, for a given false alarm probability P _Fa, can calculate first log ₁₀P _Fa, ask T as the false-alarm thresholding by (7) again, obviously calculate very simple.

Because the false-alarm thresholding T that asks by formula (7) is after supposing relevant output corresponding to each antenna, the real part of its noise and the variance of imaginary part are 1, noise is not necessarily to satisfy this hypothesis in the reality, so we adopt following formula to revise, the reason of revising is because thresholding T supposes that the variance of noise is 1, but actual noise variance is unknown, but can use

Estimate.

$T_{\mathrm{fa}}=0.5T\frac{1}{N_s}\underset{n=0}{\overset{N_s-1}{\mathrm{\Σ}}}\tilde{z}\left(n\right)---\left(8\right)$

In the output z of incoherent merging, getting length is N _sOne group of sequence z (n), length N wherein _sSize be a slot length or a subframe lengths or a plurality of subframe lengths, in (8) formula

For remove among the sequence z (n) sequence remaining after several peak-peaks according to the emulation experience, the purpose of removing peak-peak is because when the signal emission is arranged, peak-peak is sampling corresponding to useful signal, removes the rear result of these values and just is white Gaussian noise, satisfies above-mentioned series of theories.If several maximums are removed in the no signal emission, remaining sequence still is Gaussian sequence.Wherein, the factor 0.5 is that denominator is 4, rather than the degree of freedom 8 because of the mean time of asking z from y.Like this, ask after the false-alarm thresholding T according to (7) formula, ask T according to (8) formula again _FaFalse-alarm thresholding as last application.

Need to prove that the above is the situation that common logarithm is got on (5.2) formula both sides, also can take from right logarithm to (5.2) formula here.

In addition, to the degree of freedom greater than 8 Chi square of stochastic variable, come the curve of approximant (6) expression except the straight line according to formula (7) expression, other 2 points in the curve of all right modus ponens (6) expression on the near linear part, obtain other approximate straight lines, thereby obtain corresponding false-alarm thresholding according to these other near linears.

In addition, the denominator of the incoherent merging of formula (1) comprises other positive integer except 4, and the factor 0.5 in this up-to-date style (8) need change the corresponding constant coefficient factor into.For example, the denominator of the incoherent merging of formula (5.1) changes 8 into by 4, and the factor 0.5 in the formula (8) need change 1 into; The denominator of the incoherent merging of formula (5.1) changes 1 into by 4, and the factor 0.5 in the formula (8) need change 1/8 into.

Based on top false-alarm thresholding Computing Principle, the below describes the method that the false-alarm thresholding that utilizes this principle to calculate detects the PRACH targeting signal in detail, comprises the steps:

Step S1 is to the false alarm probability P of system's expectation _Fa, calculate log ₁₀P _Fa, ask the front false-alarm thresholding T of correction according to the straight-line formula (7) of false alarm probability and false-alarm thresholding;

Step S2, to having the receiver of 4 antennas, (targeting signal is that transmitter is launched one by the sequence behind the Zadoff-Chu sequence cyclic shift in ascending physical signal Random Access Channel (PRACH) to the targeting signal of receiver/transmitter simultaneously, its specific definition is seen the document 3GPP TS 36.211V8.5.0 of 3GPP LTE standard), the targeting signal that receiver receives is through the pre-process of Fig. 1 (low-pass filtering and extraction, take absolute value ask square) and press z=(y ₁+ y ₂+ y ₃+ y ₄Obtain exporting z after the incoherent merging of)/4=y/4, getting length in the output z of incoherent merging is N _sOne group of sequence z (n), length N wherein _sSize be a slot length or a subframe lengths or a plurality of subframe lengths;

Step S3 removes a small amount of several maximums among the sequence z (n) according to the emulation experience, such as 3, obtains as a result sequence

Step S4, the as a result sequence that obtains according to step S 3

The length N of sequence z among the step S2 (n) _s, the false-alarm thresholding T before the correction that obtains of step S1, utilize the correction relational expression (8) of false alarm probability and false-alarm thresholding to obtain revised false-alarm thresholding T _Fa

Step S5 judges not remove whether the false-alarm thresholding T that obtains greater than step S4 is arranged among the peaked sequence z (n) _FaValue, if having, in the targeting signal that then receiver receives random access request is arranged, if do not have, do not have random access request in the targeting signal that then receiver receives.

Above invention has been described in conjunction with most preferred embodiment, but the present invention is not limited to the embodiment of above announcement, and should contain various modification, equivalent combinations of carrying out according to essence of the present invention.

Claims (2)

1. method that detects the PRACH targeting signal comprises:

(1) to the relational expression P of false alarm probability and false-alarm thresholding _Fa(z)=e ^-2z(1+2z+2z ²+ 4z ³/ 3) take the logarithm in both sides, obtains both logarithmic relationship formulas, wherein P _Fa(z, k) is false alarm probability, and z is the false-alarm thresholding, and k is the degree of freedom, for the receiving system of 4 antennas, k=8;

(2) determine the near linear of the curve that the logarithmic relationship formula of false alarm probability and false-alarm thresholding represents;

(3) to given false alarm probability, find the solution the front false-alarm thresholding of correction according to described near linear;

(4) get that length is N in the output signal of targeting signal after incoherent merging that receiver receives _sOne group of sequence z (n), remove maximum among the sequence z (n) according to the emulation experience, obtain as a result sequence z～(n), wherein length N _sSize be a slot length or a subframe lengths or a plurality of subframe lengths;

(5) according to the correction relational expression of false-alarm thresholding Find the solution revised false-alarm thresholding, wherein T is the false-alarm thresholding before revising, T _FaBe revised false-alarm thresholding;

(6) when the value that has among the described sequence z (n) greater than described revised false-alarm thresholding, judging in the targeting signal that receiver receives has random access request, and it is characterized in that: concrete steps are:

Step S1 is to the false alarm probability P of system's expectation _Fa, calculate log ₁₀P _Fa, according to the straight-line formula of false alarm probability and false-alarm thresholding

log ₁₀(P _fa(T))=-0.6421T+1.1059

Ask the false-alarm thresholding T before revising, in the formula, T represents false-alarm thresholding, P _Fa(T) expression false alarm probability;

Step S2, to having the receiver of 4 antennas, the targeting signal of receiver/transmitter simultaneously, the targeting signal that receiver receives is through pre-process and press z=(y ₁+ y ₂+ y ₃+ y ₄Obtain exporting z after the incoherent merging of)/4=y/4, getting length in the output z of incoherent merging is N _sOne group of sequence z (n), length N wherein _sSize be a slot length or a subframe lengths or a plurality of subframe lengths;

Step S3 removes 3 maximums among the sequence z (n) according to the emulation experience, obtains as a result sequence

Step S4, the as a result sequence that obtains according to step S3

, the sequence z (n) among the step S2 length N _s, the false-alarm thresholding Z before the correction that obtains of step S1, utilize the correction relational expression of false alarm probability and false-alarm thresholding

$T_{\mathrm{fa}}=0.5T\frac{1}{N_s}\underset{n=0}{\overset{N_s-1}{\mathrm{\Σ}}}\tilde{z}\left(n\right)$

Obtain revised false-alarm thresholding T _Fa, wherein T is the false-alarm thresholding before revising, T _FaBe revised false-alarm thresholding;

Step S5 judges not remove whether the false-alarm thresholding T that obtains greater than step S4 is arranged among the peaked sequence z (n) _FaValue, if having, in the targeting signal that then receiver receives random access request is arranged, if do not have, do not have random access request in the targeting signal that then receiver receives.

2. the method for detection PRACH targeting signal as claimed in claim 1 is characterized in that, takes the logarithm in the described step (1) to be specially and takes from right logarithm or common logarithm.

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